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| United States Patent |
6,214,420
|
|
Girardin
, et al.
|
April 10, 2001
|
Process and plant for metallization of cast-iron pipes
Abstract
A plant for metallization of a metal pipe obtained by upward vertical
continuous casting and displaced vertically in a continuous manner,
includes, along the path of the pipe, a metallization station having a
passage for the pipe, a metallization enclosure (6), spray guns (11)
mounted inside the enclosure on an oscillating plate (10) surrounding the
path, means for supplying each gun with metallization material (12), and a
device for causing oscillation of the support plate and for displacing the
guns inside the enclosure with an oscillating movement, the frequency and
angular amplitude of which ensure the formation of a coating of uniform
thickness.
| Inventors:
|
Girardin; Denis (Maidieres, FR);
Lamouret; Christophe (Pont-a-Mousson, FR);
L'Huillier; Joel (Raucourt, FR)
|
| Assignee:
|
Pont-A-Mousson (Nancy, FR)
|
| Appl. No.:
|
171974 |
| Filed:
|
April 30, 1999 |
| PCT Filed:
|
April 28, 1997
|
| PCT NO:
|
PCT/FR97/00756
|
| 371 Date:
|
April 30, 1999
|
| 102(e) Date:
|
April 30, 1999
|
| PCT PUB.NO.:
|
WO97/42355 |
| PCT PUB. Date:
|
November 13, 1997 |
Foreign Application Priority Data
| Current U.S. Class: |
427/455; 118/313; 118/315; 138/145; 138/146; 427/449; 427/456 |
| Intern'l Class: |
C23C 004/08; B05C 005/04 |
| Field of Search: |
427/446,449,455,456
118/313,315,DIG. 11
219/121.47,121.53,121.58
164/459,464
138/145,146
|
References Cited
U.S. Patent Documents
| 1978415 | Oct., 1934 | Collins.
| |
| 3947607 | Mar., 1976 | Gazzard et al. | 427/37.
|
| 4690199 | Sep., 1987 | Gourmel et al. | 164/421.
|
| 4901908 | Feb., 1990 | Negura et al. | 228/183.
|
| 5133126 | Jul., 1992 | Matsuoka.
| |
| 5482734 | Jan., 1996 | Herwig et al. | 427/8.
|
| 5706866 | Jan., 1998 | Pedeutour et al. | 138/145.
|
| 5960835 | Oct., 1999 | Izaki et al. | 138/145.
|
| Foreign Patent Documents |
| 763368 | Mar., 1954 | GB.
| |
| WO 94/13472 | Jun., 1994 | WO.
| |
Other References
Patent Abstracts of Japan, vol. 7, No. 114, May 1983.
Patent Abstracts of Japan, vol. 10, No. 245, Apr. 1986.
|
Primary Examiner: Beck; Shrive
Assistant Examiner: Calcagni; Jennifer
Attorney, Agent or Firm: Sughrue, Mion, Zinn, Macpeak & Seas, PLLC
Claims
What is claimed is:
1. Process for metallization of a metal pipe obtained by vertical casting
and displaced vertically in a continuous manner with an upward movement,
comprising the steps of:
cooling the pipe in an atmosphere inert with respect to oxidation to a
temperature of 700 to 900.degree. C.; and
spraying onto the cooled pipe during the continuous, non-rotational
vertical ascent thereof, a zinc-based metallization alloy with a set of
spray guns arranged so as to surround the path of the pipe to be
metallized.
2. Process according to claim 1, wherein the zinc-based alloy is Zn.sub.x
Al.sub.1-x.
3. Process according to claim 1, wherein the metallization alloy is in the
form of a wire.
4. Process according to claim 3, wherein the said wire is a wire of an
alloy comprising between 5 and 15% of Zn.
5. Process according to claim 3, wherein the said wire is a wire of
Zn.sub.85 Al.sub.15.
6. Process according to claim 3, wherein the said wire is a lined wire
consisting of a Zn core surrounded by an Al sheathing allowing a Zn.sub.45
Al.sub.55 alloy to be obtained after melting.
7. Process according to claim 3, wherein the said wire is a lined wire
consisting of an Al core surrounded by a Zn sheathing.
8. Plant for metallization of a metal pipe obtained by upward vertical
continuous casting and displaced vertically in a continuous manner,
comprising, along the path of the pipe, a metallization station comprising
a passage for the pipe, a metallization enclosure (6), spray guns (11)
mounted inside said enclosure on an oscillating plate (10) surrounding the
path, means (20, 21) for supplying each gun with metallization material
(12), and means for oscillating the support plate and for attendantly
displacing the guns inside the enclosure with an oscillating movement,
wherein the frequency and angular movement of oscillation is selected to
ensure the formation of a coating of uniform thickness.
9. Plant according to claim 8, wherein the passage for the pipe (T) to be
coated comprises a lower part (3), a water-cooled upper part (4), a
sliding mask (5) for controlling cooling of the pipe (T) being arranged at
the joint between the lower part (3) and upper part (4), the metallization
enclosure (6) being arranged above the said upper part (4) and having
mounted on it a water-cooled casing (16).
10. Plant according to claim 8, wherein the spray guns (11) are three in
number and are arranged on the plate at 120.degree. from one another.
11. Plant according to claim 8, wherein the spray guns (11) are flame guns
or arc guns.
12. Plant according to claim 8, wherein the metallization material (12) is
a wire of ZnAl alloy and the means for supplying metallization material
comprise for each gun a wire store (20) and an unwinder (21) operated by
the oscillation movement of the plate (10) supporting the guns provided
with means for driving the wire.
13. Plant according to claim 8, wherein the metallization enclosure (6) has
a bottom (7) inclined downwards, from the centre towards the periphery and
provided with suction orifices (8), the said bottom (7) being connected at
its centre to a drop prevention cover (9) through which the pipe (T) to be
coated passes with a minimum amount of play in order to prevent the
sprayed metallization product which does not adhere to the pipe wall from
falling towards the bottom of the plant.
14. Plant according to claim 8, wherein the means for supplying each gun
(11) with metallization product (12) comprise a wire store (20) and a
device for unwinding the said wire from the store and conveying it towards
the corresponding gun (11).
15. Plant according to claim 14, wherein the wire store associated with
each gun (11) comprises a drum (22) for receiving a coil of metallization
wire provided with a central core (23) onto which the coil of wire is
threaded.
16. Plant according to claim 14 wherein the device for unwinding the
metallization wire comprises a set of wheels (30,34,38) for conveying the
wire (12) from the store (20) to above the oscillating plate (10) and a
wheel (44) for admitting into the corresponding gun (11) the wire supplied
by the set of wheels (30,34,38), the said admission wheel being mounted
oscillating on the gun in a radial direction of the said plate (10), its
orientation following the oscillations of the said plate (10).
17. Plant according to claim 16, wherein the set of wheels (30,34,38)
comprises a first wheel (30) supporting the wire (12) and mounted on a
fixed support (31), a second wheel (34) passing underneath the wire (12)
and mounted on an oscillating support (35) with which means (36,37) for
tensioning the wire (12) are associated and a third wheel (38) for
redirecting the wire (12) towards the wheel (44) for admitting the wire
into the gun (11).
18. Plant according to claim 17, wherein the unwinding device has,
moreover, between the drum (22) and the first wheel (30), an entry cone
(28) for the wire (12) and a first wire straightening device (27) and, at
the exit of the third wheel (38), a second wire straightening device (40).
19. Plant according to claim 17, wherein the means for tensioning the wire
(12) comprise a weight (37) suspended from the oscillating support (35) of
the second wheel (34).
20. Plant according to claim 16, wherein the wheel (44) for admitting the
wire (12) into the gun (11) is mounted oscillating inside a cradle (48) of
the latter by means of a fork member (51) and bearings (49,50) arranged
radially with respect to the oscillating plate (10), the bearing (50)
closest to the melting zone of the gun (11) comprising a passage (56)
through which the wire (12) passes.
21. Metal pipe obtained by vertical casting, wherein it has a metallization
coating obtained by the process according to claim 1.
22. Process according to claim 1, further comprising oscillating the spray
guns about the path of the pipe.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a process for metallization of metal
substrates and relates more particularly to the hot metallization of
pipes, in particular cast-iron pipes which are obtained by means of
vertical continuous casting.
Among the known processes for the hot metallization of pipes, the following
are known:
customized hot-galvanization;
the continuous coating of steel plates with Zn or ZnAl;
methods for thermal spraying with Zn or ZnAl alloys;
zinc-coating of pipes.
The existing solutions based on galvanization have the following drawbacks.
Customized hot-galvanization coats the pipe internally and externally and
the pipe undergoes an increase in temperature such that the results of
other prior operations carried out on the pipe at lower temperatures risk
being affected.
Hot galvanization by movement through a liquid poses the problem, currently
unsolved, of tightness with respect to the liquid bath between the
vertical pipe and the liquid metal, as well as the problem of maintaining
a bath which is clean (without matte) and has a stable composition over
time.
Cold metallization associated with annealing would ensure good distribution
if rigorous conditions for preparation of the pipe surface are satisfied
and would probably require heat treatment in an inert atmosphere.
The cost of such a treatment cycle would be considerable and as a result
would offer limited advantages from an economic point of view.
The pipe to be coated, emerging after continuous casting, is not rough,
which makes fixing of a cold coating impossible without carrying out
surface preparation.
In order to obtain a well-distributed coating, a pipe without an oxide skin
is necessary and the working temperature must be high or else the pipe
handling time must be long.
SUMMARY OF THE INVENTION
The invention aims to provide a uniformly distributed coating which has a
good impact resistance.
Moreover an object of the invention is to provide a coating which adheres
very well to the outside of a pipe of varying position and diameter,
continuously moving in a vertical direction and without undergoing
rotation, while preventing the pipe from being subject to heat annealing.
Furthermore an object of the invention is to provide a coating which is
"self-healing" in respect of any damage suffered.
Finally, an object of the invention is to provide a coating which
contributes to corrosion resistance in underground conditions.
The invention therefore relates to a process for metallization of a metal
pipe obtained by vertical casting and displaced vertically in a continuous
manner with an upward movement, characterized in that it consists in:
cooling the pipe in an atmosphere which is inert with respect to oxidation
up to a temperature of 700 to 900.degree. C.; and
spraying onto the pipe, cooled beforehand to the aforementioned
temperature, a zinc-based metallization alloy with the aid of a set of
spray guns arranged so as to surround the path of the pipe to be
metallized.
According to a particular characteristic feature of the invention, the
spray guns are made to oscillate about the path of the pipe with a
frequency and an angular amplitude adapted to the speed of displacement of
the pipe with a view to obtaining a coating of uniform thickness.
The invention also relates to a plant for metallization of a metal pipe
obtained by means of upward vertical continuous casting and displaced
vertically in a continuous manner, characterized in that it comprises,
along the path of the pipe, a metallization station comprising a passage
for the pipe, a metallization enclosure, spray guns mounted inside the
said enclosure on an oscillating plate surrounding the said path, means
for supplying each gun with metallization material and means for causing
oscillation of the support plate and for displacing the guns inside the
said enclosure with an oscillating movement, the frequency and angular
amplitude of which ensure the formation of a coating of uniform thickness.
The invention relates moreover to a metal pipe obtained by means of
vertical casting, characterized in that it has a metallization coating
obtained by the process defined above.
According to another particular characteristic feature, the spray guns are
three in number and are arranged on the plate at 120.degree. from one
another.
According to another particular characteristic feature, the spray guns are
flame guns or arc guns.
According to another characteristic feature of the invention, the
metallization material is a wire of Zn.sub.x Al.sub.1-x alloy and the
means for supplying metallization material comprise for each gun a wire
store and an unwinding device operated by the oscillation movement of the
plate supporting the guns.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be understood more fully upon reading of the description
which follows, provided solely by way of example and with reference to the
accompanying drawings, in which:
FIG. 1 is a diagrammatic, vertically sectioned view of a metallization
plant according to the invention;
FIG. 2 is a diagrammatic view sectioned along the line 2--2 of FIG. 1;
FIG. 3 is a partial diagrammatic side view of the metallization plant
according to FIG. 1;
FIG. 4 is a partially sectioned view of a flame gun of the plant; and
FIG. 5 is a micrograph of a coating obtained by the process according to
the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The metallization plant shown in FIG. 1 has, along the path of a pipe T
obtained in an upward vertical continuous casting plant (not shown) and
above this plant, a shaft 1 for passage of the pipe T being manufactured,
into which there is injected, via a duct 2, nitrogen for allowing the pipe
T to be displaced between he casting plant outlet and the metallization
plant in an atmosphere protecting the surface of the pipe T against
oxidation.
The shaft 1 has a lower part 3 which the pipe gradually cools during its
upward movement from 1100.degree. C. to 1000.degree. C. and a water-cooled
upper part 4 situated immediately below the metallization zone and inside
which the temperature of the pipe cools from 1000.degree. C. to a
temperature of between 700 and 900.degree. C.
A sliding mask 5 made of heat-insulating material is arranged inside the
shaft 1 at the level of the joint between the lower part 3 and the upper
part 4 of the latter and its movement inside the upper part 4 allows
cooling of the pipe T to be controlled by means of positioning between the
pipe and the wall of the said cooled part.
Above the shaft 1 there is arranged a metallization enclosure 6 comprising
a bottom 7 inclined downwards, from the center towards the periphery, and
provided with suction ducts 8.
In its central part, the bottom 7 is connected to a drop prevention cover 9
through which the pipe T to be coated passes with a minimum amount of play
so as to prevent the sprayed metallization product which does not adhere
to the pipe wall from falling towards the bottom of the plant.
The enclosure has moreover an oscillating plate 10 on which spray guns such
as flame metallization guns 11 are mounted.
Each gun is supplied with metallization wire 12 in a manner which will be
described with reference to FIGS. 2 to 4.
The guns 11 are for example three in number and are arranged on the plate
10 at 120.degree. from one another.
Each gun 10 sprays a jet 13 of metallization material onto the pipe T
during its upward movement.
The spray guns may also be arc guns.
They may also consist of devices for atomization of liquid metal.
Flame guns, however, have the advantage that they constitute a heat
technology which does not disturb the cooling kinetics of the product.
They ensure an excellent performance with regard to the spraying of the
atomized droplets of alloy because these droplets are not driven away from
the substrate as, for example, in the case where arc guns are used.
The flow of flame guns is finer than that of arc guns.
They require only one wire of metallization material, while two wires are
required for arc guns.
The upper wall 14 of the enclosure 6 also has suction ducts 15.
The enclosure 6 has mounted on it a water-cooled casing 16 allowing the
metallized pipe to emerge form the metallization plant at a temperature of
750.degree. C. and forming a thermal screen which prevents the plant from
becoming overheated.
The plant shown in cross-section in FIG. 2 has a platform (not shown)
through which the pipe being formed passes and on which the metallization
chamber provided with the annular plate 10 is mounted.
The plate 10 is driven in rotation with an oscillating movement by a
suitable mechanism, not shown.
As mentioned further above, in the present example, said plate carries
three flame metallization guns 11.
This number of three ensures the best compromise between the cost of the
plant and the uniformity of the thickness of the coating. However, the
number of guns may be different from three.
The amplitude of angular displacement of the plate 10 as well as its
frequency are a function of the angle of dispersion of the jets 13 of
molten metal which are sprayed by the guns 11 as well as the speed of
displacement of the pipe T so as to allow application of a metallization
layer of uniform thickness.
Each metallization gun 11 which has means for supplying oxygen and gas by
means of suitable hoses (not shown) has associated with it a device for
supplying metallization product in the form of wire 12.
Each device comprises a wire store 20 and an unwinding device denoted by
the general reference 21, intended to convey the metallization wire 12
from the wire store 20 to the associated gun 11, taking account of the
oscillating movements to which the gun 11 mounted on the oscillating plate
10 is subjected.
The wire 12 advantageously consists of an alloy containing 5 to 15% of Al.
It is also possible to use a lined wire consisting of a Zn core surrounded
by an Al sheathing, in which case, after melting, a Zn.sub.45 Al.sub.55
alloy may be obtained. The lined wire may also consist of an aluminum core
and a Zn sheathing.
The best lined wire or the best alloy is chosen in order to arrive at a
desired metallization composition of the Zn.sub.Z Al.sub.1-Z type.
FIG. 3 shows one of the spray guns 11 mounted on the oscillating plate 10
of the plant as well as the wire store 20 and the associated unwinding
device or unwinder 21.
The metallization wire 12 is positioned in coil form inside a drum 22, for
example a drum of the standard type for oil products, provided with a
central core 23 on which the wire coil (not shown) is treated inside the
drum.
Alongside the drum there is arranged a frame 25 comprising a bracket 26
which supports a wire straightening device 27 with four rollers with which
there is associated an entry cone 28 for the wire 12, directed towards the
drum 22.
At the exit of the wire straightening device 27 there is arranged a set of
wheels, a first wheel 30 of which is mounted on a slanting support 31
fixed at a point 32 of the vertical upright of the bracket 26. A second
wheel 34 is mounted oscillating about a point close to the point 32 for
fixing of the first wheel 30 by means of a movable support or bracket 35
from which a weight 36 is suspended.
The weight 36 is fixed to a rod 37 hinged on the bracket 35.
A third wheel 38 for redirecting the wire towards the plate, arranged above
the oscillating plate 10, is fixed to the structure of the plant, not
shown.
At the exit of the third wheel 38 there is provided a second wire
straigthened device with four rollers 40.
The gun 11 has mounted at its rear end, opposite to its spray nozzle 42, a
fourth wheel 44 or wheel for admitting wire into the gun, mounted on a
pivoting support and allowing modification of the inclination of the
metallization wire 12 according to the oscillations of the plate 10.
The metallization wire 12 is removed from the storage coil contained inside
the drum 22, passes through the entry neck 28, is straightened a first
time inside the straightening device 27, passes over the first wheel 30,
then underneath the second wheel 34, and then again over the third wheel
38. It is kept tensioned by the weight 36 acting on the oscillating
bracket 35 supporting the second wheel 34.
It is again straightened by the second wire straightening device with four
rollers 40 and enters into the flame gun 11 after passing over the fourth
wheel 44.
The gun 11 has a device for driving the wire so as to bring it into the
melting zone.
This device known per se and not shown comprises a servomotor with an
incorporated tacho generator, a transmission assembly with reducing gears
and pulleys for driving the wire and a device for pneumatic clamping of
the pulleys, which, by means of a piston, ensures clamping of the wire
between them.
As can be seen more clearly in FIG. 4, the flame gun 11 which has a base 46
fixed to the plate 10 is provided at its end opposite to the metallization
nozzle 42 with a cradle 48 comprising bearings 49, 50 on which a fork
member 51 supporting the fourth admission wheel 44 is mounted in an
oscillating manner.
The bearings 49 and 50 are oriented radially with respect to the
oscillating plate 10.
A guide 52 for the metallization wire 12 at the entry of the wheel 44 is
moreover mounted on the fork member 51.
The bearing 50 of the cradle 48 which is located closest to the melting
zone of the gun 42 has an axial passage 56 through which the wire 12
passes.
The gun has, moreover, connection sockets 58, 60 intended to receive hoses,
not shown, supplying the gun with gas and oxygen.
The gas used may advantageously be propane, acetylene or natural gas.
The ZnAl alloy of the wire is therefore conveyed towards the melting zone
of the spray gun 11 so as to be melted there into fine droplets and
sprayed.
The pipe T to be metallized being at the right working temperature, i.e. at
about 800.degree. C. and free from surface oxides owing to the nitrogen
atmosphere which surrounds it in the metallization zone, receives jets 13
emitted by the guns 11, consisting of a mist of ZnAl droplets which adhere
thereto.
As a result of the translational movement of the pipe together with the
alternating rotational movement of the guns 11, it is possible to ensure a
good uniformity in the thickness of the coating 62 obtained.
The alloy remains liquid on the pipe, but does not run owing to a capillary
effect and also because of the very rapid surface oxidation and surface
solidification of the external coating thus obtained.
During the entire cooling phase which follows the metallization phase and
which lasts about 15 minutes, the alloy reacts with the cast iron of the
material which forms the pipe, so as to form intermetallic compositions of
the type Fe.sub.x, Al(.sub.1-x) charged with a small proportion of
interstitial Zn.
The result obtained is a pipe coated with an external coating which is
formed such that it is continuous and perfectly adherent.
The suction system associated with the enclosure and connected in
particular to the suction ducts 8, provided in the bottom 7, and suction
ducts 15, provided in the upper wall 14 of the said enclosure, allow
recovery of the alloy droplets which have not reached the pipe.
By way of example a certain amount of numerical data relating to the
operating parameters and to the nature of the metallization alloy used is
given below.
The feed speed of the wire 12 is 3 m/min., its diameter is 4 mm and its
linear mass is 70 g/m.
The production yield is of the order of 50%.
As mentioned above, the wire is made either in the form of a Zn.sub.85
Al.sub.15 alloy or in the form of a lined wire with a Zn core, making it
possible to obtain a Zn.sub.45 Al.sub.55 alloy.
The angle of rotation of the spray guns 11 is 95.degree..
The pitch of the spraying cycle is 70 mm.
In the tests carried out it has been possible to obtain a coating of 100
g/m.sup.2 to 500 g/m.sup.2 with a Zn.sub.85 and Al.sub.15 alloy.
As shown in FIG. 5, the micrograph of a section through the coating
obtained clearly shows the formation of a well-distributed interface.
In this figure, in fact, it can be seen that a well-distributed
intermetallic interface 67 has formed between the cast-iron wall 65 and
the ZnAl coating layer 66.
During the impact tests carried out on the coated pipe it was possible to
reach values of up to 150 J, i.e. up to deformation of the pipe without
deterioration of the coating.
The corrosion characteristics of the coating obtained are on a par with
those which could be obtained by means of customized hot galvanization on
a same substrate and with the same alloy.
During coating, the pipe is not subject to any annealing effect.
The metallization process according to the invention has the following
advantages with respect to the state of the art.
It allows the thickness of the metallization coating to be controlled by
adjustment of the feed speed of the wires of metallization alloy.
It enables a continuous linear coating to be obtained.
It enables a well-distributed anti-corrosion coating to be obtained.
It allows easy application of a sealant owing to the roughness conferred to
the initially smooth pipe by the metallization coating.
Finally it allows lined wire as well as other alloys to be used.
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